Chinese Scythe Starter Rope Stuck When Spark Plug Is Installed

Hello, as per the topic.
The scythe is a Chinese one.
The resistance of the cable is so high that it is impossible to pull the cable in any way.
And nothing to start the scythe .

But the interesting thing is that if you unscrew the spark plug - i.e. there is a "hole" in the cylinder,
it can be pulled normally by the starter rope.
Screwing in the spark plug causes the cable to be blocked again somehow....

What could this be?

Hi:) What kind of scythe is it and what kind of plugs do you screw in?

Added after 2 [minutes]:

It is quite possible that you are screwing in a spark plug that is too long and not from this model because the threads fit:)

The same candle has smoked dozens of times before.
I have had this canine for a couple of years. I set up a topic because suddenly one day it won't fire.
It is a Bass Poland scythe and the candle that was purchased with it.
So the cause must be different.

Check for scratches on the cylinder. The best way is to unscrew the muffler, but you can also look through the plug hole.

Scratches would cause this?
Strange that the piston walks lightly in the cylinder when the plug is removed .

The carburettor has only one T-screw - the free idle adjustment.
The day before, I adjusted it: unscrewed a lot and lit the scythe. It had a very fast revs. I turned it off and tightened the T.
I fired it up. Still the revs were so fast that I switched it off.
I tightened the bolt some more and lit it a 3rd time.
They were still fast, but without switching off this time I adjusted the revs. The engine ran beautifully. I turned it off.

Ba the second day it was no longer possible to pull the starter cord .

Could it be that the engine was chugging along at these fast revs? And would that be the symptom of this?
If so, is there anything that can be done in this situation?
Does it remain to buy either a new cutter or a new engine?

Rycho T.,

If the head, or clutch, were out of order, would the starter cable work when the plug was removed?

And what could possibly be with the cylinder or the piston - that it would give such a symptom that the cable cannot be pulled after the plug is screwed in?

The answer is simple, these scythes get so much compression when they are ready that they are impossible to start. I often hear from customers that they are difficult to start, but the fact is that there is nothing in the engine or the starter, but there is one thing - high compression, recently the boss allowed us to insert decompression valves for such cases, and it is much easier, but the cost is considerable, 200 PLN including the valve.

Rycho T. wrote that after screwing in a plug it is even easier to turn, because of the reduced compression. So according to this when I unscrew the spark plug, I increase the compression?
In my opinion it is rather the other way around. Because when I unscrew the spark plug, according to me there is no compression there. That's why the piston runs lightly and you can pull the starter rope without resistance.
Compression is, after all, pressure, and if there is no spark plug then there is a hole and no pressure.

So what you wrote @ helena33 makes sense to me.

Rycho T. is a great authority for me – so I don't know what to think about it anymore….

For now, I accept the opinion @ helena33. It is logical to me. The huge compression puts such resistance that I am not able to pull the line .

What you wrote @ helena33 about Bass Poland scythes „getting so much compression after running-in that they actually can't be fired up just like that”, corresponds well with such a sentence from wikipedia about compression:
„Too high compression pressure usually means wear of the sealing rings. This is associated with additional sealing of the sealing rings by means of engine oil passed over them through the scraper rings.”

What is puzzling, however, is that, as you wrote, it helps „to insert decompression valves.”
I wonder for how long?
Because this increased compression is not without cause after lapping…
And if the cause is similar to the one described in wikipedia, will such a treatment help for long?

P.s..
Besides, I know from experience with this scythe that if I fix one thing in it, even on the same day another one falls down .
Hands are falling...
It's probably not worth making and I'm already looking around for another one.
However, I was curious to find out what it was about the cable, as even at the service centre they had no idea. And they returned it after a week without repairing it.

And here you are right mate Kusep, not everyone is as enthusiastic as you are, the mechanic who repairs these Chinese machines knows that it is crap, and putting a decompression valve is just a placebo, because the rings will break sooner or later, so do as you write, buy something better, but I will not recommend anything, about what is now good and not Chinese you can read on the forum. Greetings

Please, correct errors. Rycho T .

Many thanks @ helena33 .
Points fly for the earlier factual explanation.
And without the need to unbolt the scythe, I learned the answer

The moral of this is that Chinese scythes work until they arrive

The reply @ Rych T. confirms indirectly such a cause, because from his diagnosis comes the info that the engine is not seized. And that's also what I thought, since the piston goes lightly in the cylinder when there is no plug. And why look for cracks in that case?

Is this scythe a two-stroke? If so, the theory of oil sealing the rings (ot a different lubrication system) is out. It's just arrived and has a good comprecha or the starter is too small in diameter. I also have an old Shtil saw and it has a factory decompressor, which I don't need at the moment as the compression is already gone due to wear.

Two-stroke, of course. After all, Chinese crap .

Good observation with that ring.
On the other hand, it's a bit abnormal for the compression to not allow the engine to start after lapping…
But as @helena33 wrote on Bass Poland scythes, I guess that's what's normal.

On the other hand, two questions arise:
1) Is that why other manufacturers give decompressors, so that this does not happen with their scythes? That is, so that starting is possible after the engine has been run-in?
2) Do they only give decompressors to make starting lighter? As they just write.

Why does lapping increase the compression in the engine so much?
For me to produce a scythe that cannot be started after lapping is just plain cheating…

It's like this. The scythe would suddenly arrive after a few years. Strange. To me it seemed to happen for the first 5l of fuel. By adjusting this screw you have depleted the mixture - the consequence of swelling and/or deformation of the piston shell.

But why does the piston walk lightly when the spark plug is removed?
If it was swollen would it walk?

P.s.
Earlier, me and @helena33 went a bit off topic and the admin, on the occasion of deleting @helena33's post, deleted it together with a passage strictly on topic. I am therefore quoting it (I have kept a record of the page on disk as I expected this):

helena33 wrote:

This is because in these Chinese engines there are large to excessive piston diameters, and quite large piston jumps after passing the exhaust window, resulting in huge compression after running-in.

Maybe it has swollen just enough to compress more strongly?
The one without a spark plug - no compression - goes on lightly?

Write whether it is as Rycho T wrote.

Unscrew the exhaust and carburettor. Then try it. I've been through several branded saws and scythes and somehow the compression didn't rise in any of them. I am sure it is a mechanical failure. You can try spinning behind the magneto by removing the starter.

I'll unscrew that exhaust and carburettor and then give it a try, as I'm very curious.
/I already have a second scythe.
Well, and all in all a question worth solving.

Rycho T wrote:

If there is that much compression, then even then, pulling the string would slowly move the piston upwards until past the top position.
Then, the resistance would decrease until the next compression. Write down if this is the case.

.

I unscrewed the spark plug, but didn't drip too much as to where the top position was. Something was seemingly moving, but the pen - which I used as a gauge - always went in at the same depth.

However, I think it is as you wrote, Rychu, because while pulling the line I noticed that it can be pulled out every 5-6 cm, and after 5 cm there is a sudden resistance.... the line stops suddenly and I can't move it forward.... However, if I wait a while, it is possible to pull out again at 5 cm.... and so on....

This is much more likely what Rycho T writes. I agree with this statement, because when a scythe or other Chinese tool has compression it has, but without exaggeration that you can no longer turn the shaft at all. With the kind of damage that Rycho T writes about, there should be a knocking noise (like breaking glass) when you unscrew the spark plug, it will be easier for you to verify. If such a noise comes from the engine, it means that one of the shaft or connecting rod bearings has a problem with the pressure caused by compression.
As others have written and I have written, you still need to take it apart and look at it, there's no harm in it now mate, you've got a new goat and you can practice repairs on this one .